If you're wondering what constitutes a "Golarion monster," stick to things that (1) fit with the Golarion setting, (2) have a reasonable expectation that it could be found on Golarion, regardless if its home is elsewhere.
A phase spider is a "Golarion monster" even though its home is on the Ethereal plane.
A flumph is a "Golarion monster" even though its home is the Dark Tapestry.
An akata is a "Golarion monster" even though it comes from another planet (it flies through space and lands on other worlds).
Golarion is an inclusive setting--it has guns, vikings, genies, ninjas, mothmen, dragons, and all sorts of crazy stuff... but it's still a fantasy campaign setting. But it doesn't really have steampunk, post-apocalyptic, or other nonstandard fantasy genres (ignore Numeria for the purpose of this discussion). If your monster idea is something that's only found on the Plane of Fire, or on planet Castrovel, or in the future, and never found elsewhere/elsewhen, those aren't really "Golarion monsters" and you should rethink your concept.

I assume you're talking about the line break between "Poison (Ex)" and the rest of the poison info. If the vorin looks like that, the vorin is wrong. Check the following Bestiary monsters to see how they match the provided format: venomous snake, naga (any), quasit, phase spider...

LIMITATION: Entry cannot be or use a monster template (fiendish, lich, and so on).

Since Bestiary 3, fey is now both a creature type and a template. And if I wanted to make a fey creature, my natural instinct would be to look at the elements in the template and see what i could use. How do we distinguish and avoid getting disqualified?

Construct (banned): Something constructed from non-living (or no longer living) material. (Only slightly blurry line for things like the Retriever (a spider-like thing from the abyss) and certain golems that look undead-ish.)

Undead: It's either: a) something alive that died and was brought back in whole or in part with negative energy; b) something that was born undead; or c) something that is comprised of compressed entropy / negative energy

Humanoid: basically human in shape, generally with no/few special abiities, no extra limbs, and near-human intellect. Usually almost exactly like a human or with only slightly animalistic characteristics

Fey: Pretty much exclusively humanoid in shape (though often much smaller in size). They either have a very close tie to nature (in that they are nature spirits, in some way), or they originally hailed from The First World. Elves, Gnomes, and a few others straddle the line between fey and humanoids. I often muse about why goblinoids and Orcs aren't fey, but that's more of a lore thing.

Hardest to ClassifyMagical Beast: Some large/intelligent animals, beasts that combine animal features (griffons, chimerae, extra heads), normal animals with special abilities, animals with extra body parts (horns, wings, more than 4 limbs), and other animal-like things that don't exist in the real world. Blurry lines with Vermin, Animals, and Monstrous Humanoids.

Monstrous Humanoid: There seems to be a blurry line with normal humanoids and magical beasts (think of the difference between a sphinx and a lamia), but it generally has at least a human-like upper torso (especially hands and a face/head), and features that can be connected to an animal of some sort. It most often has powerful special abilities above that of a human, which raises its CR.

Aberration: A catch-all for things that don't fit in the other categories. They are typically: a) creatures from another planet; b) related to an elder god; c) horrifically mutated results of spells, science, a god's wrath, or other unnatural circumstances; d) something that would otherwise be a magical beast or monstrous humanoid that isn't for some reason (good indicators are that it lives underground, has tentacles, or combines the features of animals, vermin, oozes, and/or plants in some weird way)

No, I put in a flurry of last minute changes. Raised the dex...and then the Int...and made it a bonus feat...and changed Flight to Fly...and added a semi-colon I'd missed...and changed modifiers...and altered some minor language so as not to repeat adjectives so much...chewed my nails down over word count...hoped the mechanic I used works...altered movement rate again...and nat armor...changed the skills...changed them again...